1. Field of the Invention
The present invention relates to a controller for a cylinder cut-off type internal combustion engine which can switch a full cylinder operation which operates all of a plurality of cylinders and a partial cylinder operation which cuts off the operation of some of the plurality of cylinders, and purifies exhaust gas from some cylinders and the remaining cylinders with catalysts provided in two exhaust systems independently of each other.
2. Prior Art
A controller for a cylinder cut-off type internal combustion engine of the type mentioned above is known, for example, in Laid-open Japanese Patent Application No. 8-17742. This cylinder cut-off type internal combustion engine is switched in operation between a full cylinder operation with all of a plurality (six) of cylinders and a partial cylinder operation with some (three) of the plurality of cylinders. The cylinder cut-off type internal combustion engine also comprises exhaust air pipes connected to some cylinders and the remaining cylinders, respectively, catalysts provided respectively in these two exhaust pipes, and a communication pipe for communicating the two exhaust pipes with each other at a location upstream of the catalysts. A valve mechanism is further disposed at a location downstream of the catalyst in the exhaust pipe associated with the remaining cylinders for opening and closing the exhaust pipe.
This controller fully opens the valve during the full-cylinder operation such that exhaust gas from the some cylinders and the remaining cylinders through the respective exhaust pipes. During the partial cylinder operation, on the other hand, the controller reduces the opening of the valve such that a portion of exhaust gas from the remaining cylinders is exhausted through the exhaust pipes of the remaining cylinders, while the remaining portion of the exhaust gas is guided to the exhaust pipes of the some cylinders through the communication pipe, and exhausted therethrough. In this way, the catalysts in the some cylinders are heated by the exhaust gas exhausted from the remaining cylinders to maintain its active state, so that the emission characteristics are maintained in a favorable state when the engine is switched from the partial cylinder operation to the full cylinder operation.
However, the foregoing conventional controller for a cylinder cut-off type internal combustion engine operates the valve even if the catalysts are fully activated, irrespective of the temperature of the catalysts in the some cylinders, causing extra power consumption. Also, a reduced opening of the valve results in a larger exhaust resistance and accordingly a loss of the engine power. As a result, the fuel consumption rate is degraded. Furthermore, the controller requires the communication pipe, the valve, and a mechanism for driving the valve.
The present invention has been made to solve the problems mentioned above, and its object is to provide a controller for a cylinder cut-off type internal combustion engine which is capable of ensuring an activated state of catalysts in cylinders, which are stopped during a partial cylinder operation, at all times to maintain favorable emission characteristics upon switching from the partial cylinder operation to a full cylinder operation, and is also capable of maintaining a satisfactory fuel consumption rate by conducting the partial cylinder operation to the utmost.
To achieve the above object, the present invention provides a controller for a cylinder cut-off type internal combustion engine which can be switched between a full cylinder operation in which a plurality of cylinders are all operated and a partial cylinder operation in which some of said plurality of cylinders are prohibited from operating. The cylinder cut-off internal combustion engine adapted to purify exhaust gas from said some cylinders and from the remaining cylinders with first and second catalysts provided respectively in two exhaust systems independent of each other. The controller includes catalyst temperature detecting means for detecting a temperature of said first catalyst, and partial cylinder operation disabling means for disabling said partial cylinder operation when the detected temperature of said first catalyst is lower than a predetermined temperature.
According to this controller for a cylinder cut-off type internal combustion engine, the partial cylinder operation is disabled when the detected temperature of the first catalyst is below the predetermined temperature to transition to the full cylinder operation. As a result, the exhaust gas from the some cylinders and the remaining cylinders is supplied to the first and second catalysts, respectively, thereby making it possible to prevent the temperature of the first catalyst from lowering to the inactive state. Since this ensures the activated state of the first catalyst at all times, favorable emission characteristics can be maintained when the engine is switched from the partial cylinder operation to the full cylinder operation. Also, since the partial cylinder operation is performed unless the temperature of the first catalyst is below the predetermined temperature, a favorable fuel consumption rate can be ensured. It should be noted that in this disclosure, xe2x80x9cdetection of the temperature of the catalystxe2x80x9d is not limited to directly detecting the temperature of the catalyst with a temperature sensor or the like, but includes estimating the temperature of the catalyst in accordance with an operating state of the cylinder cut-off internal combustion engine.
Preferably, the foregoing controller further includes operating state detecting means for detecting an operating state of said cylinder cut-off type internal combustion engine, wherein said catalyst temperature detecting means includes catalyst temperature estimating means for estimating the temperature of said first catalyst based on the detected operating state.
According to this controller, the temperature of the catalyst can be estimated in software without the need for adding special parts, mechanisms and so on such as a temperature sensor for sensing the temperature of the catalyst, a communication pipe, a valve and a driving mechanism therefor, and so on, which are required in the prior art, thereby making it possible to save the manufacturing cost.